Traveling Abroad with a Non-U.S. Passport from the U.S.
The United States does not mandate strict exit controls, which means you are not strictly required to have any passport as a condition for leaving the country. However, travelers of any nationality leaving the U.S. through an international airport or land border normally do not undergo passport verification to check citizenship or visa status.
US Citizens and Non-U.S. Passports
Notwithstanding these general principles, there are specific requirements for U.S. citizens. The U.S. law stipulates that U.S. citizens may use only a U.S. passport when entering and leaving the country in situations where a passport is required. This is mainly due to the need to comply with other countries that mandate passport checks for entry.
For commercial aircraft and other vessels, the carrier is legally mandated to verify documents that assure the traveler will be admitted to the destination country. This is not an exit control and does not require U.S. citizens to present a U.S. passport. A U.S. dual citizen, for instance, may present a non-U.S. passport when leaving the U.S.
Common Practices in International Travel
Millions of people leave the U.S. every year on non-U.S. passports. They do this for various reasons, including as tourists, businesspersons, and even permanent residents holding green cards. The practice of using non-U.S. passports for international travel is quite common around the world. Each country issues passports to its own citizens, and it is legally permissible for individuals to carry and use such passports when traveling to or from a country other than the U.S.
US Citizens and Foreign Passports
U.S. nationals, including dual nationals, are required to use a U.S. passport to enter and leave the U.S. However, using a foreign passport to travel to or from a country other than the U.S. is not inconsistent with U.S. law. For U.S. citizens, it is required to enter and leave the U.S. using a U.S. passport. Although there are usually no overt exit formalities, your airline will check your documents when you check in for a flight, and this information will be transmitted to CBP (Customs and Border Protection). Therefore, the U.S. government will be aware if you have used a foreign passport.
In conclusion, while there are no strict exit controls in the U.S., U.S. citizens are generally required to use a U.S. passport for travel. However, individuals from other countries are quite free to use their respective passports for entry and exit from the U.S. If you have any specific questions about international travel or passport requirements, consult with a travel professional or consult the official U.S. Department of State website for the most up-to-date information.